Try start Firefoxin Safe Mode: *[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-using-safe-mode Firefox in safe mode] I think this can be a corrupted file, so try create a new profile: *[https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles?esab=a&s=profile&r=0&as=s Use the Profile Manager to create and remove Firefox profiles] Also: *[https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware Problems caused by malwares] *[https://support.mozilla.org/en-US/kb/remove-recent-browsing-search-and-download-history Clear recent history] *[https://support.mozilla.org/en-US/kb/how-do-i-create-screenshot-my-problem Create a screenshot of the problem]

Hello MHK-JAN, also, in your system details it seems that you have in your [http://kb.mozillazine.org/Profile_folder_-_Firefox#Windows profile folder] a [http://kb.mozillazine.org/User.js_file User.js] file. The user.js file does not exist by default. If you create the file, forget it, if you have not create the file then delete the User.js file (some programs create and write in the file also). thank you

You can try to set the browser.sessionhistory.max_total_viewers to 0 (default = -1) on the <b>about:config</b> page. *http://kb.mozillazine.org/about:config

I removed user.js, but did not work